This invention relates to pressure indicators and, more particularly, to pressure indicators for pneumatic tires and the like which provide a visual warning of under-inflation.
Pneumatic tires are typically rated for use within specified pressure ranges selected to provide optimum tire wear and safety. Notwithstanding the improvements that have been made over the years in pneumatic tire materials and designs, tires still have a tendency to lose air pressure with use. The extended operation of a vehicle with one or more under-inflated tires can be costly as well as hazardous, particularly at relatively high speeds. For example, it is a known fact that under-inflated tires decrease vehicle fuel mileage and wear more quickly than properly inflated tires. Under-inflated tires can also adversely effect the maneuverability and control of the vehicle. In extreme conditions of under-inflation, tires can become so overheated as to weaken and become increasingly susceptible to sudden failure or blow-out. Since losses due to tire under-inflation can be very high in terms of cost of equipping and operating a vehicle as well as in terms of possible injury to the occupants of the vehicle, damage to cargo or to the vehicle itself, it is very desirable to provide means for indicating tire under-inflation so that it may be corrected before the vehicle is operated. It is also desirable that tire under-inflation reliably be detected by a relatively simple visual inspection of the vehicle and corrected without excessive effort.
A wide variety of pressure indicators have been previously proposed for use with pneumatic tires. Many of these indicators are designed to provide the operator of a vehicle with a visible warning as soon as a tire under-inflation condition occurs. However, in spite of the recognized utility of these indicators, none of them has experienced widespread commercial acceptance. Several reasons apparently account for this lack of acceptance.
Firstly, many of the known pressure indicators have relatively complex constructions and are thus relatively expensive. As a result, many vehicle owners and operators prefer to use conventional methods of checking tire pressure with a pressure gauge in spite of the time and inconvenience required therefor rather than equip their vehicles with the costly indicators.
Other known indicators lack sufficient reliability to justify their use in lieu of conventional pressure checking methods. In some cases, the indicators give false warnings of low tire pressure due to normal variations in tire pressure with use of the vehicle and force the vehicle operator to waste time verifying the warnings. In other cases, the indicators fail to indicate low tire pressure conditions when they occur. If the vehicle operator relies upon the indicators, the vehicle may be operated despite an under-inflated tire causing damage to the tire and other, possibly more serious, damage. These malfunctions are partly due to poor indicator designs and partly due to the wear and tear experienced by the indicators as a result of being carried by the tire and exposed to various road hazards. For example, many indicators malfunction because they fail to seal out water, road dust, dirt, oil, grease and the like which tend to interfere with the internal mechanisms thereof.
Perhaps the most significant and difficult-to-solve problem accounting for the lack of widespread use of prior pressure indicators stems from their inability to provide a reliable and effective seal for the air pressure in the tire. Because the sealing arrangements used have not been totally effective, air leaks through the indicators. With many such indicators, the leakage becomes even more rapid after they are actuated to signal a tire pressure drop. These indicators thus aggravate the very condition they are intended to eliminate.